The motions of DNA macromolecules affect the rates of the process of replication and transcription, and thus rates of growth and metabolism. Using recently developed sensitive and fast electro-optic (E-O) instrumentation, which includes an on-line digital computer for data acquisition and processing, we plan to measure the dynamical motions of intact DNA from various cells under a wide variety of solvent conditions, particularly in the presence of mutagenic dyes, carcinogens, various antibiotics and antitumour agents. Various parameters characterizing the spectrum of relaxation times of the internally flexible macromolecules will be computed. The mean relaxation time, the width of the spectrum, and its shape will be sensitive to the local and long-range flexibility of the macromolecule, as well as its length. Therefore the relaxation properties will lead to information regarding the effects of the binding on the DNA rigidity or flexibility. The data will be evaluated and correlated with other known properties of the complexes of DNA with known mutagens, carcinogens, therapeutic agents and strongly binding drugs, such as LSD-25, which causes chromosomal damage. Experiments will be done to evaluate and exploit the sensitivity of the E-O relaxation technique to the measurement of UV and gamma-ray radiation damage of DNA, and of supercoiling in circular DNA. Theories of intercalation and of other modes of binding, will be examined. Correlations with biological activity will be sought.